Waste heat boiler



Aug. 2, 1932. A, HUET 1,870,009

WASTE HEAT BOILER Filed March 1. 1929 7' f l Fig .1'.

'WiJ/c@ A TTORNE Y.

Patented Aug. 2,L 1932 UNITED STATE-s PATENT OFFE ANDRVHUET, F PARIS, FRANCE, ASSIGNOR TO THE SUPEBHEATER COMPANY, 0F

` NEW YORK, N. Y.

WASTE HEAT IBOILER Application led March 1, 1929, Serial No. 343,602, and in France July 27, 1928.

In installations l'comprising reversing furnaces (gas heated furnaces, metallurgical furnaces, Cowpers, etc.) the flues carry alternately hot gases (000 to 8000 centigrade) i and cold gases (80 to 100 0.), the reversing periods being of very variable lengths. Attempts have been made for a long time to recuperate the very considerable amount of heat carried by such gases and various re- 0 cuperative installations have in fact been made for this purpose. Une of these solutions-the simplest one in principleconsisted in using the gases iiowing from the furnaces for heating a boiler directly, but

the following difficulty was encountered: To utilize the sensible heat of the gases which are alternately hot and cold and to produce steam, the boiler must of necessity absorb heat when the gases are hot but must not give up their heat or any part of it when the gases are cold.

In other words, the heat interchanger constituting the boiler heating surface must pern mit the transmission of heat only in the direction from the hot gases to the boiler and not in the direction from the boiler to the cold gases so that the surface must act in the manner of check valves used for controlling the flow of fluid or electrical check '30 valves (generally called heterodynes) which permit the current to pass in only one direction. lt is easy to see that the ordinary types of boilers with water tubes or smoke tubes are useless in this connection.

The present invention has for its object a heating process and an apparatus making it possible to obviate this difficulty, and applicable quite generally to any type of recuperation of heat contained in fluids whose tem- 40 perature may vary within wide limits. This process consists in using an irreversible transmission of the heat to the water of the boiler by means of an intermediate circuit of con- A densable fluid, using for this purpose an in- 5 stallation analogous to that described in United States application 303,474 filed on Sept. 1, 1928.

In practice, if a cold curr-ent passes over the part of the primary circuit extending into the flue, the fluid condenses almost entirely and the circulation is immediately practically arrested.

Neglecting the small losses due to conduction, all transfer of heat from the boiler to the heating fluid ceases, since the intermediate agent no longer circulates.

If, now, onewishes to recuperate the heat in different fines in which gases circulate whose temperature is variable above and below the saturation temperature corresponding to the boiler pressure, a closed circuit containing an intermediate condensable fluid is placed into each flue, all the flues being assumed to have in them points of temperature higher than the saturation temperature corresponding to the boiler pressure.

For purposes of simplification, all the primary circuits might eXtend into the same drum or boiler and thus if it is desired a plurality of flues might contribute to a single steam generation.

In particular, in thecase of a reversing recuperating heating system, there will always be at least two flues in which there are alternately hot and cold point-s.

A single boiler provided with two primary circuits will be able to furnish a substantially constant steam production by drawing heat lternately from one or the other of the two ues.

The description which follows and which makes reference to the accompanying draw ing given by way of example, will make clear the manner in which the invention may be carried out.

Fig. l represents diagramlnatically an assembly of such an installation applied to three flues;

Fig. 2 is a section on line 2-2- of Fig. l;

Fig. 3 is a combined diagram of th-e temperature variations in the three lues plotted against time.

rlhe primary circuits comprise the vaporiz* ing tube bundles 1, the steam risers 2, the condensing coils 3 located in the drum T and the downcomers 4 for the condensate.

The vaporizing bundles are arranged in parallel between lower water'headers 5 for the return of the condensate and the intermediate steam collectors 6.

The water vaporized in the bundles l is condensed in the coil 3 and is returned to the circuit by the return tubes 4.

The combined eiect of the thermo-Siphon and the result of the vacuum created by the condensation in the coils 3, creates an intense circulation of the primary Huid which may attain considerable velocity, thus producing a high rate of heat interchange.

In other words, the thermal eiiciency of such a vaporizing system is very high.

It one of the tlues should now have cold gases passing through it, the corresponding circuit l ceases to vaporize. The condensation ceasing in the corresponding condensing coil, the motive power disappears and circulation is arrested. No convection any longer exists in the circuit, and as a consequence no heat transfer from the water of the boiler T toward the cold gases occurs.

The losses resulting from the metallic conduction of the structure are in practice negligible. Thus, the e'l'ect et a heat check valve has been obtained.

vF ig. 2 is a section on line 2-2 oiz one of the primary circuits shown diagrannnatically in Fig. 1;

Fig. 3 shows a diagram of the temperature results plotted against time t', in each of the iues the alternation of hot and cold gases being assumed to occur at regular intervals, the base line for the temperature being the minimum temperature, this being assumed to be the same as that in the lines. The dot and dash line parallel to the time axis shows the temperature corresponding to the pressure of the boiler. The temperatures obtaining in each flue at any given moment are the ordinates or the three curves corresponding to the same abscissa, and the diagram shows a heat transfer to the boiler with very small variations, the hot and cold gas passages in the various tlues having been properly equalized.

It is obvious that modifications in the details may be made in the process just described without going outside of the trame of the invention.

I claim:

l. In apparatus of the class described, the combination of a container :tor fluid to be heated, a duct located at a lower level than the container, means at times during normal operation causing a ilow through the duct of a fluid above the temperature to which it is desired to heat the Huid in the container and at other times causing a. flow through the duct of a fluid below said temperature, and a heat transferring unit constituting a closed circuit partially lilled with liquid a portion of the circuit extending into the duct and a second portion extending into but not opening into the container.

2. In apparatus of the class described, the combination of a steam generating drum7 a duct at a lower level than the drum, means to at times during normal operation cause a flow through the duct of gases having a temperature higher than that corresponding to the pressure at which steam is to be generated in the drum and at other times of gases of a lower temperature, and a heat transferring unit constituting a closed circuit and comprising a heat absorbing portion extending into the duct, a heat delivering portion extending into but not opening into the drum, portions connecting the two first named portions to permit upward and downward circulation, and a liquid in said unit but onlypartially illing it.

3. In apparatus of the class described, the combination oi a steam generating drum, a plurality of ducts at a lower level than the drum, means associated with each duct to at times during` normal operation cause a flow of gases through the duct of a temperature higher than that corresponding to the pressure at which steam is to be generated in the drum and at other times oi gases of lower temperature, the said times of hot gas flow through the ducts not coinciding with each other; a plurality of heat transferring units each constituting a closed circuit and coml prising a heat-receiving portion extending into a duct, a heat-delivering portion eX- tending into but not opening into the drum, and portions connecting the two first-named portions to permit upward and downward circulation, each unit being partially filled with a liquid; there being in each duct one or more heat receiving portions.

ANDR HUET. 

